Symmetric multiprocessing system with unified environment and distributed system functions

In a data processing system including a plurality or functional units connected from a system bus and competing for access to the system bus, an arbitration means for determining access to the system, comprising:

• a plurality of arbitration lines;
• in each functional unit,
• a mask latch means having inputs connected from the arbitration lines wherein the inputs of the mask latch means or the functional units are shifted relative to one another for receiving and storing an arbitration mask having an entry representing the shifted input to the arbitration lines, the location of the entry representing the relative priority of the functional unit,
• an arbitration latch means having unshifted inputs connected from the arbitration lines to receive and store arbitration signals asserted by the functional units,
• a control means for performing alternating arbitration signal latch cycles and arbitration resolution signals and responsive to the latched arbitration signals in the arbitration latch means and to the mask in the mask latch means for
• identifying the functional unit as a member of a group when the function unit asserts an arbitration signal in the same latch cycle as at least one other functional unit,
• determining from a comparison of the latched arbitration signals and the mask the priority of the functional unit,
• determining when the functional unit is the highest priority member of the group,
• asserting an arbitration signal until the functional unit is the highest priority member of the group,
• asserting control of the system bus when the functional unit is the highest priority member of the group, and
• ceasing to assert the functional unit arbitration signal at completion of the bus operation.